In a lubricating structure of an internal combustion engine, generally, oil is pumped up from an oil pan by an oil pump, and fed to respective portions of the internal combustion engine through oil passages diverging from a main gallery. As this type of lubricating structure of the internal combustion engine, there has been known a lubricating structure of an internal combustion engine in which oil is directly fed from a main gallery to a bearing of a shaft requiring high oil pressure (e.g. see JP-UM-A-4-107543). The internal combustion engine according to JP-UM-A-4-107543 uses a two-shaft balancer structure in which balancer shafts are disposed on front and rear sides of a crankshaft. Oil passages extending toward bearings of the front and rear balancer shafts or bearings of various transmission shafts diverge from the main gallery which is high in oil pressure. As this type of lubricating structure of the internal combustion engine, there has been known a lubricating structure of an internal combustion engine in which oil having lubricated a valve device such as a camshaft inside a cylinder head is returned to an oil pan through a cam chain chamber where a cam chain is received (e.g. see JP-A-10-054296). In the internal combustion engine according to JP-A-10-054296, a valve chamber in which the valve device is received and the cam chain chamber are made to communicate with each other, and the oil which has lubricated the valve chamber flows down into the cam chain chamber to be returned to the oil pan.